Relational Quantum Mechanics and the PBR Theorem: A Peaceful Coexistence

TL;DR

This paper demonstrates that Relational Quantum Mechanics (RQM) remains compatible with the PBR theorem by analyzing foundational assumptions, clarifying that RQM's epistemic view of the wave function does not conflict with PBR's conclusions.

Contribution

It clarifies the compatibility of RQM with the PBR theorem by analyzing foundational assumptions and discussing the limitations of deriving a relational PBR-type result.

Findings

RQM's epistemic view is compatible with PBR theorem

Implicit assumptions about ontic states in PBR are incompatible with RQM

A relational PBR-type result cannot be derived

Abstract

According to Relational Quantum Mechanics (RQM) the wave function $\psi$ is considered neither a concrete physical item evolving in spacetime, nor an object representing the absolute state of a certain quantum system. In this interpretative framework, $\psi$ is defined as a computational device encoding observers' information; hence, RQM offers a somewhat epistemic view of the wave function. This perspective seems to be at odds with the PBR theorem, a formal result excluding that wave functions represent knowledge of an underlying reality described by some ontic state. In this paper we argue that RQM is not affected by the conclusions of PBR's argument; consequently, the alleged inconsistency can be dissolved. To do that, we will thoroughly discuss the very foundations of the PBR theorem, i.e. Harrigan and Spekkens' categorization of ontological models, showing that their implicit assumptions about the nature of the ontic state are incompatible with the main tenets of RQM. Then, we will ask whether it is possible to derive a relational PBR-type result, answering in the negative. This conclusion shows some limitations of this theorem not yet discussed in the literature.